1. Field of the Invention
The present invention relates to a wafer handling apparatus and in particular relates to a wafer feeder adapted for wafer feed in a vacuum enclosure.
2. Description of the Related Art
Conventionally, in order to perform a wafer exchange operation, as shown in FIG. 9 and FIG. 10, equipment is known in which a blade 74 carrying a wafer is mounted at the tip of an arm 71 comprising a pair of freely bendable bending links 72, 73 which are symmetrically arranged, the base ends of bending links 72, 73 being supported so that they are rotatable in the peripheral direction, and the base ends of these bending links 72, 73 being respectively driven in rotation by drive motors 77, 78 and magnetic couplings 75, 76 arranged on two vertical levels. Since bending links 72, 73 have respectively independent drive axes, the equipment is constituted so as to sense their operations individually. Also, in the case of equipment where a plurality of arms 71 are arranged vertically, a complicated construction is provided below the arms to synchronize vertical drive of the arms in order to cut the number of drive axes.
Also, in the case of a single-direction double arm constituted such that a plurality of arms perform extension/retraction operation individually and towards a station in one direction, the blades of the upper and lower arm overlap during arm contraction, so, since it is not possible to use a transmission type sensor to identify on which blade the wafer is mounted, a reflective type sensor is arranged close to the blades.
However, the above prior art construction was subject to the problems that complicated control was required and the cycle time was made long since the operations of each drive shaft were sensed individually. Also, there was the problem that the swiveling radius became large due to the provision of a complex synchronization mechanism below the arm, and, with increasing wafer size, there was the problem that the mechanism itself tended to become of large size due to the need to strengthen the arm links, and a heavy object had thus to be raised and lowered.
Also, if a reflective type sensor was arranged close to the blade, there was the risk of interference with the wafer, blade or arm, etc. There was also a problem of unstable sensing occasionally caused by color differences on the surface of the wafer. To deal with these problems, a transmission type sensor could be arranged at some point along the path of extension/retraction of the arm and at each station, so as to detect which arm was extended and whether a wafer was placed thereon, but, if this was done, when the arm was driven, there was a risk of spurious detection due to the arm or blade passing over the transmission type sensor. This meant that the arm had to be stopped midway, or a time restriction monitored by a timer had to be imposed, leading to the problems of complicating the control operation and lowering the reliability of wafer sensing.